1. Field of the Invention
The present invention relates to an apparatus and method for controlling power generation in a hybrid vehicle which comprises an engine and an electric motor as a power source for driving the vehicle. In particular, the present invention relates to a technique for controlling power generation amount when the engine is idling.
2. Description of Related Art
Conventionally, hybrid vehicles which carry motors as power sources for driving the vehicles in addition to engines are known. Hybrid vehicles are divided into series hybrid vehicles and parallel hybrid vehicles. In the series hybrid vehicles, the engine drives a generator whose electric power output is used to drive the motor, which in turn drives the wheels. In this case, because the output of the engine is not mechanically connected to the driving wheels, the engine can be constantly driven within an engine-speed range of a high fuel mileage and a low emissions level. Therefore, the series hybrid vehicles can achieve lower fuel consumption and lower emissions levels than conventional engine vehicles.
In contrast, in the parallel hybrid vehicles, as is disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 7-123509, a motor is mechanically coupled to an engine so as to assist the rotation of the drive shaft of the engine. The motor can also act as a power generator to generate electrical power, and the generated electrical energy is stored in a battery. The electrical energy charged in the battery can be supplied to electrical equipment and so on in the vehicle.
In this case, although the output of the engine is mechanically connected to the driving wheels, drive loads on the engine can be reduced. Therefore, the parallel hybrid vehicles can also achieve lower fuel consumption and lower emissions levels than conventional engine vehicles.
The parallel hybrid vehicles can be divided into several types. One is a type in which a motor is connected to an output shaft of an engine so that the motor can assist the output of the engine, and such as when the vehicle decelerates, the motor acts as a generator to charge a battery, etc. Another is a type in which both or either of a motor and an engine can generate driving force, and a generator is independently provided.
These hybrid vehicles perform various controls, for example, when the vehicle accelerates, the motor assists the output of the engine, and when the vehicle decelerates, the motor generates electric power by deceleration regeneration to charge a battery, etc. Therefore, it is possible to constantly maintain electrical energy (the remaining battery charge) in the battery and to respond to the demands by the driver of the vehicle. For example, Japanese Unexamined Patent Application, First Publication No. Hei 7-123509 discloses such a control technique.
In the above-described hybrid vehicles, when power assistance by the motor is not necessary, the motor regenerates electric power to charge a battery. This regeneration of electric power is performed not only when the vehicle decelerates but also when the engine is idling. That is, even when the engine is idling, the motor is rotated by the idling: engine acting as a generator.
However, when the engine is idling, should the total torque load of the load for the power generation by the motor, the load generated by a creep state of an automatic transmission system, and the load for activating an air conditioner, etc., be greater than the torque generated by the engine, there arises a problem that the engine will stall. In particular, when the hybrid vehicle is at high altitudes, this problem occurs more easily because the intake pressure of the engine is lower. If the idling speed of the engine is increased in order to prevent the engine from stalling, there arises another problem that the fuel consumption of the engine will undesirably increase.
Moreover, when starting the vehicle from the idling state, the hybrid vehicle controls the drive motor by automatically selecting one mode from an assistance mode in which the motor assists the output of the engine in accordance with demands, and a non-assistance mode in which the vehicle runs only by the driving power from the engine while charging a battery by the motor. For example, when a relatively large torque is required at the time of starting the vehicle, the assistance mode is selected, and when large torque is not required, the non-assistance mode is selected. Accordingly, depending on the conditions, the motor performs assistance of the driving power.
However, in the case where the non-assistance mode is selected when starting the vehicle, the engine drives the motor to generate electric power, and the generated electric power is charged in the battery. Therefore, the load for driving the motor (that is, power generation torque) is applied to the engine in addition to the torque for driving the vehicle, and the problem arises that smoothness at the time of starting the vehicle will be degraded.
The object of the present invention is to provide an apparatus for controlling the power generation torque applied to an engine by a motor in accordance with a state of the hybrid vehicle.
In order to achieve the above object, a power generation control apparatus according to the first aspect of the present invention comprises: a detection device which detects a state of the hybrid vehicle in which a torque load to be applied to an engine of the hybrid vehicle should be decreased; and a generation amount control device which decreases the generation amount to be generated by a motor when the state of the hybrid vehicle is detected.
A hybrid vehicle according to another aspect of the present invention comprises: an engine which outputs a driving force for the hybrid vehicle; a motor which outputs an assistant driving force so as to assist the driving force of the engine; a power storage unit which supplies electric power to the motor when the assistant driving force is necessary, and which stores electric power generated by the motor when the assistant driving force is not necessary; and a power generation control apparatus which controls the power generation by the motor. The power generation control apparatus comprises: a detection device which detects a state of the hybrid vehicle in which a torque load to be applied to an engine of the hybrid vehicle should be decreased; and a generation amount control device which decreases the generation amount to be generated by a motor when the state of the hybrid vehicle is detected.
A power generation control method according to another aspect of the present invention comprises: a first step of detecting a state of the hybrid vehicle in which a torque load to be applied to an engine of the hybrid vehicle should be decreased; and a second step of decreasing the generation amount to be generated by a motor when the state of the hybrid vehicle is detected.
According to these aspects, a state of the hybrid vehicle in which a torque load to be applied to an engine of the hybrid vehicle should be decreased is detected, and the generation amount to be generated by a motor is decreased. Therefore, engine stall can be prevented and a smooth start of the vehicle is possible.
The another object of the present invention is to provide an apparatus for controlling the power generation torque applied to an engine by a motor in accordance with a necessary load when in an idling state.
In order to achieve the above object, a power generation control apparatus according to the first aspect of the present invention comprises: a load torque calculation device which calculates load torque to be applied to an engine of the hybrid vehicle for generating electrical power used in the hybrid vehicle when the engine is idling; a generable torque calculation device which calculates torque generable by the engine when the engine is idling; and a power generation load torque determination device which determines a limiting value of a power generation load torque to be applied to the engine in accordance with the load torque calculated by the load torque calculation device and the generable torque calculated by the generable torque calculation device.
According to this power generation control apparatus, when the torque generable by the engine is decreased in proportion to the decrease in the air-intake pressure of the engine, the power generation load torque applied to the engine by the motor is controlled so as to decrease depending on the decrease in the torque generable by the engine. Therefore, engine stall can be prevented. Additionally, in the case where the power generation by the motor decreases in accordance with the decrease in the torque generable by the engine, because the battery is used for compensating the shortage of the electric power, it is not necessary to increase the idling speed of the engine. Therefore, deterioration of the fuel consumption can be prevented.
A hybrid vehicle according to another aspect of the present invention comprises: an engine which outputs a driving force for the hybrid vehicle; a motor which outputs an assistant driving force so as to assist the driving force of the engine; a power storage unit which supplies electric power to the motor when the assistant driving force is necessary, and which stores electric power generated by the motor when the assistant driving force is not necessary; and the aforementioned power generation control apparatus which controls the power generation by the motor.
The another object of the present invention is to provide an apparatus and method for controlling the power generation in hybrid vehicles by which the smoothness of starting the vehicles can be improved even when a non-assistance mode accompanied with power generation is selected at the time of starting the vehicle.
In order to achieve the object, a power generation control method according to another aspect of the present invention comprises: a first step of detecting if the state of the engine has shifted from an idling state to a non-idling state; and a second step of temporarily decreasing the generation amount to be generated by the motor when the state of the engine is detected to have been shifted from the idling state to the non-idling state.
According to the above method, when the state of the engine is shifted from the idling state to the non-idling state, the generation amount by the motor is temporarily decreased, and the load applied to the engine by the motor for the power generation is diminished. Therefore, while the generation amount is suppressed, the load torque applied to the engine can be diminished.
The non-idling state is for example a starting state of the vehicle. In this case, the output of the engine can be effectively used for accelerating the vehicle, and it is possible to smoothly start the vehicle from the idling state.
In the first step, it is preferable to detect a starting operation for shifting a state of the engine from an idling state to a running state (mode) accompanied with power generation. In general, the charging of the battery is carried out during a running mode in which the load applied to the engine is relatively light. Therefore, for example, by detecting the change of the engine load, the starting operation at the time of shifting the driving mode from the idle mode to the running mode accompanied with power generation can be detected. In this way, by detecting that the mode is the running mode accompanied with power generation, it is possible to avoid unnecessary power generation control during a running mode which is not accompanied with power generation (for example, in the assistance mode). Therefore, control of the power generation can be effectively performed.
In the second step, it is preferable to temporarily halt the charging of the power storage unit so as to decrease the generation amount by the motor. In this case, the load applied to the engine in order to generate electric power for battery charging is omitted. Therefore, the start of the vehicle can be smooth.
A power generation control apparatus according to another aspect of the present invention comprises: a detection device which detects if the state of the engine has shifted from an idling state to a non-idling state; and a generation amount control device which temporarily decreases the generation amount to be generated by the motor when the state of the engine is detected to have shifted from the idling state to the non-idling state.
The detection device preferably detects the starting operation for shifting the state of the engine from an idling state to a running state accompanied with power generation. Preferably, the generation amount control device temporarily halts the charging of the power storage unit so as to decrease the generation amount by the motor.
According to this apparatus, when the state of the engine is shifted from the idling state to the non-idling state, the generation amount by the motor is temporarily decreased (for example, for 0.5 to 1 second), and the load applied to the engine by the motor for power generation is diminished. Therefore, while the generation amount is suppressed, the load torque applied to the engine can be diminished, and a smooth start of the vehicle is possible.
Here, in the case where the above non-idling state is the starting state, that is, in the case where the state of the engine is shifted from the idling state to the starting state, the detection of the starting state is preferably carried out as follows:
(1) The change of the mode between the idle mode and the other modes is detected.
(2) The change of a gear position to an in-gear state is detected.
(3) The release of a brake is detected.
In the case of (1), for example, it is possible to detect the starting operation in a manual transmission car which does not comprise a switch for detecting a gear position. The discrimination between the idle mode and the other mode can be carried out based on the degree of throttle opening, an air intake passage pressure, an engine speed, etc. By means of detecting the change of the driving mode based on such information, the starting operation from the idling state can be detected.
In the case of (2), for example, it is possible to detect the starting operation in an automatic transmission vehicle (a CVT vehicle or an AT vehicle) which comprises a switch for detecting a gear position. When an automatic transmission vehicle starts, because the gear position is shifted from an N-range (neutral) or a P-range (parking) to a D-range (drive), by means of detecting the change of the gear position, the starting operation from the idling state can be detected.
In the case of (3), if a brake is in an ON state, the brake will be released by a driver to start the vehicle. Therefore, by means of detecting the release of the brake, the starting operation from the idling state can be detected.
In the present invention, it is also possible to detect the starting operation based on, for example, the change of the engine load. In this case, not only the detection of the starting operation, but also non-assistance modes such as a cruise mode can be detected, and it becomes possible to control the generation amount in accordance with the driving mode.
In the present invention, the concept xe2x80x9cstarting statexe2x80x9d includes the release of a brake, the driver""s operation (starting operation) such as the shift of a gear position, and a state of the vehicle itself such as the change of the engine load. That is, the concept xe2x80x9cstarting statexe2x80x9d includes all states of movement relating to the start of the vehicle.
Furthermore, a hybrid vehicle according to another aspect of the present invention comprises: an engine which outputs a driving force for the hybrid vehicle; a motor which outputs an assistant driving force so as to assist the driving force of the engine; a power storage unit which supplies electric power to the motor when the assistant driving force is necessary, and which stores electric power generated by the motor when the assistant driving force is not necessary; a detection device which detects if the state of the engine has shifted from an idling state to a non-idling state; and a generation amount control device which temporarily decreases the generation amount to be generated by the motor when the state of the engine is detected as being shifted from the idling state to the non-idling state.